This invention relates to gene therapy. More particularly, this invention relates to a plasmid system for increased expression of vascular endothelial growth factor (VEGF) under hypoxia conditions. The plasmid system can be used for treating ischemic disease in a person in need of such treatment, such as a person in need of treatment for ischemic heart disease.
Gene therapy with VEGF is a new treatment of ischemic diseases, such as ischemic heart disease. The delivery of the VEGF gene to ischemic heart has been achieved using naked DNA injection, polymeric carriers, and retrovirus, adenovirus, or adeno-associated virus carriers. M. Azrin, Angiogenesis, protein and gene delivery, 59 Br. Med. Bull. 211-215 (2001); J. M. Isner, Myocardial gene therapy, 415 Nature 234-239 (2002); J. Kastrup et al., Vascular growth factor and gene therapy to induce new vessels in the ischemic myocardium. Therapeutic angiogenesis, 35 Scand. Cardiovasc. J. 291-296 (2001). Naked DNA injection is safe, since it does not induce cytotoxicity or severe immune response. Previous reports have shown that naked plasmid delivery of the VEGF gene is effective in the treatment of ischemic myocardium. J. F. Symes et al., Gene therapy with vascular endothelial growth factor for inoperable coronary artery disease, 68 Ann. Thorac. Surg. 830-836, discussion 836-837 (1999); P. R. Vale et al., Left ventricular electromechanical mapping to assess efficacy of phVEGF(165) gene transfer for therapeutic angiogenesis in chronic myocardial ischemia, 102 Circulation 965-974 (2000); C. Sylven et al., Myocardial Doppler tissue velocity improves following myocardial gene therapy with VEGF-A165 plasmid in patients with inoperable angina pectoris, 12 Coron. Artery Dis. 239-243 (2001). However, injection of naked plasmid suffers from low efficiency of gene expression. J. M. Isner, supra.
To improve efficiency of plasmid delivery, polymeric gene carriers have been developed. These polymeric gene carriers include TerplexDNA and water-soluble lipopolymer (WSLP). D. G. Affleck et al., Augmentation of myocardial transfection using TerplexDNA: a novel gene delivery system, 8 Gene Ther. 349-353 (2001); M. Lee et al., Hypoxia-inducible VEGF gene delivery to ischemic myocardium using water-soluble lipopolymer, 10 Gene Ther. 1535-1542 (2003). These polymeric gene carriers increased the transfection efficiency to myocardium up to tenfold. In addition, the duration of gene expression was prolonged compared to naked DNA. The prolonged duration of gene expression by polymeric carriers may be due to the ability of the carriers to protect DNA from nucleases. However, these polymeric carriers may be cytotoxic to cells and still have lower transfection efficiency than viral carriers.
Another approach to gene delivery is to use retrovirus, adenovirus, or adeno-associated virus as a gene delivery vector. Virus-mediated gene transfer showed high gene transfer and expression activities. It is generally accepted that a viral carrier is the most efficient way to transfer therapeutic genes. However, virus-mediated gene transfer may lead to immunogenicity or host chromosomal integration, suggesting possible mutagenesis. M. Azrin, supra. In addition, the production of viral particles for encapsulating the DNA is not as cost-effective as that of naked DNA or polymeric carriers.
Therefore, each delivery method has its own advantages and disadvantages, and the selection of a gene carrier is largely dependent on its availability and the target disease.
Another concern with respect to gene therapy using VEGF is the gene regulation system. Currently, VEGF is the most effective therapeutic gene for neo-vascularization. J. M. Isner, supra. Previously, it was reported that both VEGF and its receptors were upregulated in ischemic tissues. E. Brogi et al., Hypoxia-induced paracrine regulation of vascular endothelial growth factor receptor expression, 97 J. Clin. Invest. 469-476 (1996). Therefore, it was suggested that ischemia is necessary for VEGF to exert its effects. J. S. Lee & A. M. Feldman, Gene therapy for therapeutic myocardial angiogenesis: a promising synthesis of two emerging technologies, 4 Nature Med. 739-742 (1998). However, Springer et al. proved that exogenously delivered VEGF could exert a physiological effect in normal, non-ischemic tissue. M. L. Springer et al., VEGF gene delivery to muscle: potential role for vasculogenesis in adults, 2 Mol. Cell 549-558 (1998). In addition, unregulated continuous expression of VEGF is associated with formation of endothelial cell-derived intramural vascular tumors. R. J. Lee et al., VEGF gene delivery to myocardium: deleterious effects of unregulated expression, 102 Circulation 898-901 (2000). This suggested that VEGF expression must be regulated. Therefore, an erythropoietin (Epo) enhancer was used to enhance VEGF gene expression locally in ischemic tissues. It was shown that the Epo enhancer and the SV40 promoter enhanced VEGF gene expression under hypoxia condition in human embryonic kidney 293 cells in vitro and in rabbit ischemic myocardium in vivo. M. Lee et al., supra. In addition, Su et al. proved that a hypoxia-responsive element (HRE) mediated VEGF expression in ischemic myocardium, using adeno-associated virus as a gene carrier. H. Su et al., Adeno-associated viral vector-mediated hypoxia response element-regulated gene expression in mouse ischemic heart model, 99 Proc. Nat'l Acad. Sci. USA 9480-9485 (2002). In this trial, the VEGF gene was regulated by the hypoxia response element (HRE) and the SV40 promoter. This regulated VEGF expression system should be useful for safer VEGF gene therapy, minimizing unwanted side effects.
In view of the foregoing, it will be appreciated that providing a plasmid for gene therapy of ischemic disease, wherein the plasmid expresses VEGF under regulated control and can be delivered with a polymeric carrier, would be a significant advancement in the art.